1. Technical Field
The present invention relates to digital circuits in general, and in particular to digital timing circuits. Still more particularly, the present invention relates to a digital timing circuit for measuring time of arrival of an asynchronous event.
2. Description of the Related Art
Certain applications require a determination of the arrival time of an asynchronous event. For example, the precise distance between a laser source and a target can be ascertained by determining the time of flight for a laser light to travel from the laser source to the target. The time when the laser light hits the target is considered as an asynchronous event. Other applications include locating a vessel by measuring the time of flight of an electromagnetic signal from three reference transponders to the vessel that carries a fourth transponder.
Most prior art digital timing circuits utilized to perform any of the above-mentioned timing determination are typically not very precise. Common solution for increasing the precision of prior art timing circuits may include increasing the stability of reference clocks, increasing the speed of reference clocks, eliminating sources of certain kinds of jitter, etc. Although such solutions have been successful in a few applications, they are also very expensive to implement. In addition, such solutions have physical limitations as to how fast a reference clock can be made. Consequently, it is desirable to provide an improved digital timing circuit for measuring time of arrival of an asynchronous event. The digital timing circuit should be able to accurately measure the time of arrival of an asynchronous event without relying on expensive clock circuits.